ACPAtmospheric Chemistry and PhysicsACPAtmos. Chem. Phys.1680-7324Copernicus GmbHGöttingen, Germany10.5194/acp-9-3755-2009Synoptic influences on springtime tropospheric O<sub>3</sub> and CO over the North American export region observed by TESHegartyJ.1MaoH.1TalbotR.11Institute for the Study of Earth, Oceans and Space, Climate Change Research Center, University of New Hampshire, Durham, New Hampshire 03824, USA1106200991137553776This work is licensed under a Creative Commons Attribution 3.0 Unported License. To view a copy of this license, visit http://creativecommons.org/licenses/by/3.0/This article is available from http://www.atmos-chem-phys.net/9/3755/2009/acp-9-3755-2009.htmlThe full text article is available as a PDF file from http://www.atmos-chem-phys.net/9/3755/2009/acp-9-3755-2009.pdf

The relationship between synoptic circulation patterns over the western
North Atlantic Ocean in spring (March, April, and May) and tropospheric
O<sub>3</sub> and CO was investigated using retrievals from the Tropospheric
Emission Spectrometer (TES) for 2005 and 2006. Seasonal composites of TES
retrievals reprocessed to remove the artificial geographic structure added
from the a priori revealed a channel of slightly elevated O<sub>3</sub> (>55 ppbv) and CO (&gt;115 ppbv) at the 681 hPa retrieval level between
30&deg; N and 45&deg; N extending from North America out over the Atlantic
Ocean. Ozone and CO in this region were correlated at <i>r</i>=0.22 with a slope
value of 0.13 mol mol<sup>&minus;1</sup> indicative of the overall impact of
photochemical chemical processes in North American continental export.
Composites of TES retrievals for the six predominant circulation patterns
identified as map types from sea level pressure fields of the NCEP FNL
analyses showed large variability in the distribution of tropospheric
O<sub>3</sub>. Map types MAM2 and MAM3 featuring cyclones near the US east coast
produced the greatest export to the lower free troposphere with O<sub>3</sub>>65 ppbv and a relatively well-defined O<sub>3</sub>-CO correlation (slope
values near 0.20 mol mol<sup>&minus;1</sup>). The ensembles of HYSPLIT backward
trajectories indicated that the high O<sub>3</sub> levels were possibly a result
of pollutants lofted to the free troposphere by the warm conveyor belt (WCB)
of a cyclone. An important finding was that pollutant export occurred in the
main WCB branch to the east of the cyclone and in a secondary branch
circling to the back of the cyclone center. Conversely, a map type featuring
a large anticyclone dominating the flow over the US east coast (MAM6)
restricted export with O<sub>3</sub> levels generally &lt;55 ppbv and CO levels
generally &lt;110 ppbv. There was also evidence of stratospheric intrusions
particularly to the north of 45&deg; N in the 316 hPa composites
predominately for MAM1 which featured a large cyclone near Newfoundland.
However, the concurrence of these intrusions with pollutant export,
specifically in the southwestern North Atlantic Ocean, made it difficult to
delineate their respective contributions to the 681 hPa O<sub>3</sub> composites.